Fibrous apatite has been grown by the enzymatic hydrolysis of calcium beta-glycerophosphate on reconstituted calfskin collagen tapes which had been modified by the addition of a phosphoprotein, phosvitin, in the presence of a cross-linking agent, dimethylsuberimidate. The deposits were identified as a carbonate-bearing hydroxyapatite by x-ray diffraction, and scanning electron micrographs confirmed their fibrous character.